PURPOSE: To prevent the crushing and powdering of a reforming catalyst due to the shrinkage of each reforming tube in a reformer by cooling at the time of stopping the reformer by allowing gas to flow in the reforming tube at such a flow rate as to suspend the reforming catalyst.

CONSTITUTION: Hydrocarbon such as fuel oil or natural gas is allowed to react with steam by heating in the presence of a reforming catalyst in a fuel reformer to obtain mixed gas consisting essentially of H2, CO, CO2, CH4 and steam. At the time of stopping the reformer, gas is allowed to flow in each reforming tube 1 formed into cylindrical or plate-fin shape and packed with the reforming catalyst 2 at such a flow rate as to suspend the catalyst 2. The void of the catalyst packed layer is increased and the crushing and powdering of the catalyst 2 due to the shrinkage of the tube 1 by cooling can be prevented.